In a typical wireless network, many devices can communicate with each other. To facilitate communications between multiple networkable devices, communications must be managed. Thus, each network typically has a communications controller such as an access point, a piconet controller (PNC), or a station that acts as a controller to manage network communication. A PNC can be defined as a controller that shares a physical channel with one or more stations where the PNC and stations form a network. Each station, such as a personal computer, can associate with the controller and thereby associate with the network. Associating with the network can include connecting to the network. Getting authorized by the network and gaining access to resources that are available via the network connection. Stations and network controllers typically utilize a network interface card (NIC) to handle the association process and to facilitate communication between the network devices. To increase system efficiency, some wireless networks utilize omni-directional transmissions for the association process and directional transmissions for data exchange.
Many wireless networks utilize a frequency of 2.4 GHz for communicating, as defined by the Institute of Electrical and Electronics Engineers ((IEEE)) 802.11b and g specifications. Other wireless networks utilize a frequency of 5 GHz for communicating as defined by the IEEE 802.11a specification. IEEE 802.11a and b were published in 1999, and IEEE 802.11g was published in 2003. Due to the number of networks, and crowded airways in these frequency ranges, additional wireless networks standards are being defined where such networks can communicate utilizing millimeter waves producing frequencies of around 60 GHz. With such high frequencies, directional communications are being considered to achieve acceptable performance for the expected link budget requirements.
The Federal Communications Commission (FCC) limits the amount of power that a computer network type transmitter can emit. Both omni-directional transmissions and directional transmissions are anticipated for these networks that utilize millimeter wave transmissions. An omni-directional transmission generally provides a traditional radiation pattern where the signal energy evenly propagates (unless obstructed) in a spherical manner. In contrast a directional transmission can focus signal energy in a particular direction. A directional transmission can allow a network to operate more efficiently because more energy can be sent in the direction of a receiver while less energy is sent in directions where the signal is not intended to be received. Generally directional antennas have gains that are much higher than omni-directional antennas due to the narrower beam width, which focuses radio frequency power towards the receiving system. As stated above such a configuration does not waste nearly as much radio frequency (RF) power in directions where there are no receiving devices.
Likewise, a receiver can focus it's receive sensitivity in a particular direction. Thus, a transmitter can focus RF energy in a direction of a receiver and a receiver can focus receive sensitivity in a particular direction to mitigate interferences and increase communication efficiency. This is particularly important when such low power levels are utilized among many different types of interference. A directional transmission system can provide improved performance over omni-directional systems due to the increased signal strengths between devices and decreased interference from devices transmitting from directions where the receiver is less sensitive.
Thus, the omni-directional mode utilizes a relatively low data rate transmission on the order of a few Megabits per second to compensate for the loss of antenna gain. However higher data rates, on the order of a few Gigabits per second, are possible in a directional transmission mode since the directional link employs directional antennas and benefits from higher antenna gains. However, these directional systems are typically more complex and more expensive than traditional omni-directional transmission systems.
In addition to the omni-mode and directional-mode, network devices can also transmit in a wideband mode and in a narrowband mode. Thus, communication channel management can be based on the concept of narrowband and wideband channels where wideband channels can include more than one narrowband channel.
Since device locations (or relative locations of devices) in a piconet are not known on start up, the piconet can be formed utilizing a single narrowband channel. Accordingly, this single narrowband channel can be utilized for communication management. Communication management can include beaconing, device discovery, probes, association requests and acknowledgements, and other control/management messages. According to current and proposed specifications, these network management control transmissions are performed in the single narrowband omni directional communication format as described above. Once a device is associated with a network, the device can exclusively occupy a wideband channel and utilize high data rate, beamformed directional data communications.
This type of channelization can cause major problems when piconets are transmitting in different narrowband channels in the same wideband channel. When this occurs, omni mode transmissions in the narrowband channel can cause significant interference with data transfers between devices taking place in the directional mode in a wideband channel. Thus, such interference occurs even if such communication is done after beamforming.